The present invention broadly relates to protective coverings for equine hooves and, more particularly relates to a therapeutic support horseshoe made from non-metallic polymeric material formed to include an inner side surface and an outer side surface between the opposing hoof-contacting and ground-contacting surfaces a slot formed in the inner side surface, approximately halfway between the opposing hoof-contacting and ground-contacting surfaces, and extending from the one caudal end to the other caudal end.
Wild horses rarely suffer from lameness unless they are injured in some way. This is true mainly due to the fact that they are constantly on the move, run on uneven ground, stand in water and otherwise are exposed to environmental factors which wear away the hoof in the manner in which nature intended. The hoof mechanism in its natural state is designed to be a shock absorber as well as a vital aid to the circulatory system. When in motion, on contact with the ground surface, the digital cushion is compressed between the pastern bone and the sensitive frog and redirects the remainder of the force outwards and upwards to the lateral cartilages (attached to the sides of the coffin bone). The foot will expand and the sole will widen, this expansion absorbs shock and also permits the coffin bone to lower which in turn brings blood flow to the area. As the foot is lifted in stride it contracts forcing the blood out of the foot and up the leg as the foot hits the ground on the next stride. Not only does the entire structure of the foot benefit from increased circulation this process is fundamental for the health and wellbeing of the horse.
Domesticated horses are not so lucky. They are exposed to much less uneven terrain and spend a great deal more time confined to stalls where movement is prohibited as the average stall is 11′×11′. They are protected from the more harsh and abrasive aspects of nature. Furthermore, special feeds which create other desirable conditions in domesticated horses may have a harmful effect on the feet. Therefore, it has long been recognized that special care is required to maintain domesticated horses' feet in proper condition. Horseshoes are used for this purpose.
Traditionally over the years most domesticated horses have been and are currently shod with shoes made of metal such as steel or aluminum alloys.
Horseshoes are typically secured to hooves by nails. The nails pass through holes in a horseshoe and are driven into the horn wall of the hoof, or hard keratinous portion. Great care must be taken in directing the nail into the hard keratinous portion so as to prevent injury to the horse. The nails are driven at an angle away from the center of the hoof, the nail points extend through the outer side wall of the hoof where they are cut off and clinched or hammered against the hoof.
Aluminum alloys are most commonly used today in racing and are characterized by efficient application, relatively low weight and expense. Horses engaged in competition training or racing are commonly re shod every three to six weeks depending on the individual's hoof growth. This is done in consideration of the weakened clinches (nails), but primarily by the desire to maintain healthy geometry with respect to the configuration of the foot and so facilitate optimal biomechanics, or way of going. As a result of the natural flexion and movement of the foot over time the nails work loose and the clinches become raised, which can often lead to a horse dislodging a shoe or shoes. This event can result in damage to the hoof wall when the clinched nails are pulled through the wall of the hoof or more disastrous if the shoe is not pulled off cleanly the horse may step on exposed nail ends damaging the sole or frog or further damage a leg with the dislodged shoe.
Frequent removal and reattachment of shoes makes numerous nail holes in the hoof walls. There is always a possibility of error when driving a nail, if driven too close to the white line it can be very painful for a horse leading to lameness and possibly abscesses. If there is insufficient new healthy horn growth two problems arise. First, with numerous nail holes already in the hoof wall, it can be difficult or sometimes impossible to secure a new shoe. Second, the abundance of nail holes lets in bacteria, dries out the hoof wall, damages the corium (vascular tissue that supplies nourishment to the hoof) and generally weakens the hoof structure, which can lead to failure of the wall and damage to the horse's hoof and foot. Thus, the well-known phrase, no foot no horse, prevails.
The surfaces on which horses train and perform vary widely. Horses frequently train and compete on grass, dirt, sand, cinder, crushed stone, and sometimes on packed surfaces which nearly approach the hardness of asphalt or cement. The hardness of the training or racing surfaces can greatly increase the effective rate of loading, thus the shock and vibration, e.g., the peak g forces which the horse will experience. The shock and vibration transmitted to a horse's anatomy is intensified by metal shoes and can directly affect a horse's efficiency, athletic performance and the amount of trauma that will be experienced.
Accordingly, it can be readily understood that the potential for injury is large whenever horses train or race on hard surfaces. Horses are best trained by placing them into open paddocks and training them on forgiving yet not unstable natural surfaces. Clearly, no single factor can so greatly affect the level of stress being placed upon a horse, as can the training or racing surface and overall training program. In Thoroughbred or Standardbred racing, trainers have very few alternatives other than utilizing a racetrack for daily training.
It is known that the foot of an active unshod horse living in a natural environment will wear such that the front and back of the hoof become gently rounded. In fact, horseshoes which are initially substantially rectangular in cross-section will wear in these areas and eventually enable the combination of a horse's foot and horseshoe to assume a somewhat similar shape. Unfortunately, many conventional horseshoes are so constructed as to require replacement by the time this more natural configuration is attained.
It is also known that the hoof of an active unshod horse living in a natural environment will assume a slightly concave shape in the toe area between the medial and lateral sides, as when viewed from the front, but also along both sides of the hoof between the toe and heel. This configuration permits the hoof to better slide or plane over the ground support surface during the braking phase as impact takes place, thereby reducing the effective rate of loading and the shock and vibration experienced.
Further, this configuration permits the hoof to better grab the surface during the later propulsive phase, and to break over and make a faster transition during toe-off, thus enhancing stride frequency and exhibited speed. The ability of the horse's hoof to slide somewhat can also enhance stability relative to a situation in which a horse's foot would suddenly catch or grab the ground support surface, as can happen with the use of horseshoes having rectangular configurations which possibly further include toe grabs, raised traction members or cleats. Of course, the presence of extremely loose or slippery ground can neutralize the possible adverse effects of such traction devices, and in fact, such may provide better performance and safety in such circumstances.
As mentioned, it is known that in the unshod natural state, a horse's foot and hoof will flex and slightly widen when under load forces. It follows that use of relatively rigid metal or aluminum horseshoes substantially prevents this natural movement and so tends to reduce both the effective size, and the shock and vibration absorbing capability of a horse's foot. A steel horseshoe is known to be more forgiving in this regard than an aluminum horseshoe. For that matter, it is believed that the occurrence of hoof cracks is sometimes caused by the flexing and widening action of the foot and hoof working against the nails associated with a substantially inflexible horseshoe. Inflexible horseshoes also are known to prevent the natural wearing of the hoof, which can result in contraction and inflammation of the foot.
Non-metallic materials such as plastic or rubber are sometimes used in combination with a metal horseshoe and such hybrid products are generally referred to in the industry as bonded horseshoes.
Plastic and rubber materials have been chemically and/or mechanically bonded to metal shoes to create various configurations, e.g., these materials have been used between upper and lower metal layers of a horseshoe, between the horseshoe and the hoof, on the ground engaging portion of a horseshoe, and to completely encapsulate a metal horseshoe.
Although some shock or vibration may be relieved through these alternatives, the rigidity of the metal shoe is still present as is the damaging effect of the nails.
Horseshoes made entirely of plastic material are known. Most, if not all, plastics-fabricated horseshoes currently on the market, however, suffer from the disadvantage that they are time-consuming and awkward to apply, particularly those that have to be assembled from a kit of parts or require special equipment. The composition of plastic horseshoes varies widely with some being as restrictive as a metal horseshoe. And while some inventions teach methods where a person without farrier skills can attach the hoof covering, equine hooves require particular preparation prior to shoe application such that unknowledgeable trimming or rasping and handling of some equipment can realize disastrous results. For that matter, such unskilled farrier practice on most Thoroughbred horses, especially those in intensive training programs, can easily result in injury.
Furthermore, some glue-on horseshoes currently on the market require attaching the glue-on horseshoe using side extensions such as tabs or fabric cuffs which extend up the sidewall of the hoof. Gluing to a sidewall presents special problems, principally because bonds there can be subjected to very high tensile forces when a horse pivots, and bonds are usually weakest in tension. In addition, for horses with thin hoof walls, such as many Thoroughbreds have, when gluing side extensions the high heat (hoof adhesives heat up significantly when curing) can produce discomfort for the horse. The hoof wall is almost encapsulated by these extensions and adhesive, creating unnatural conditions which can be detrimental to the health of the horse's foot.
For that matter, it is time consuming to fit such a shoe, wasteful of material, and requires a number of parts to be supplied for each shoe. For the next shoeing, the tabs can prove extremely difficult to remove from the upper hoof wall, causing discomfort for the horse and extra time spent prepping the hoof for the fitting of new shoes.
Prior art has not recognized a product made from a plastics material which is widely accepted by trainers of performance horses. The foregoing illustrates limitations known to exist in present horseshoes. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming the limitations set forth above.
The present invention offers a solution where prior art has failed. Two of the foremost problems are addressed by the invention, the eradication of a rigid shoe and nails as the form of attachment. For example, the invention provides horseshoes which conform to the foot imitating the known configuration which healthy, active, unshod horses acquire when living in a natural environment. The horseshoes are configured with a degree of hardness closely resembling the natural composition of the equine hoof that permits natural flexing and widening of the foot and horseshoe when under load forces.
The horseshoes offer many advantages including without limitation a significant reduction of trauma and stress subjected to the horse's skeletal and muscular system when under load forces and improved circulatory system thus enhanced performance and health of the horse.
Due to the characteristics of the present invention, a self-levelling effect in the horseshoe is achieved. That is, in horses shod with the inventive horseshoes, as new horn is regenerated over the course of a few weeks, the horseshoe gradually wears, resulting in a longer period of optimal biomechanics before the next shoeing. The heels are allowed to drop naturally as they grow avoiding the jammed up effect which can often lead to quarter cracks.
The invention also provides an improved method of attaching a horseshoe using adhesives, which eliminates nails, promotes stronger, healthier horn regeneration and removes the element of error when driving nails. The horseshoes can be easily and efficiently attached or removed by a farrier in the field, as it may be cut, rasped, sanded or ground down using regular farrier tools. For that matter, the horseshoes considerably reduce occurrence of diseases and detrimental conditions of the foot, e.g. laminitis, navicular syndrome, white line disease and quarter cracks.
The inventive horseshoes are easily fitted to a foot having a given shape and width by cold forming without the need for special equipment. The horseshoes are neither bulky nor obtrusive, are light and comfortable for the horse and being attached by adhesive guards against dislodgment regardless of the direction of frictional force on the shoe relative to the hoof. For that matter, field testing has proven its strength and resilience by 6 weeks of continued attachment on a Thoroughbred racehorse in an intensive training program, producing winners on racing surfaces, dirt, synthetic and turf.
The invention includes one or more embodiments of therapeutic horseshoes configured for use in treating angular deformities and/or for compensating for various deleterious effects to the foot and hoof that can sometimes occur during known treatments for serious angular deformities.
Various limb deformities in foals, weanlings and yearlings, including angular deformities, can be treated at an early stage surgically and/or with foot care to correct the deformity or at least improve the prognosis as the horse matures. Angular limb and flexure deformities are common limb abnormalities manifest in foals that require early recognition and treatment. Foals with angular limb deformities, i.e., valgus and varus deformities, have traditionally been referred to as “knock-kneed” or “bow-legged” in the front limbs. A valgus deformity is defined as a deviation of the limb away from the midline (knock-kneed). A varus deformity is a deviation of the limb toward the midline (bow-legged). The most common location of angular limb deformity is the carpal joint (knee).
As is known, a growing horse's foot changes shape in response to weight distribution and varying a weight distribution. A side of the hoof that is lined up closer to the vertical line of force (bone column) develops a straighter vertical wall and the opposite site develops a more sloping wall and in more severe cases, develops a flare. As the vertical wall becomes more vertical it fails to provide adequate support. In some cases, the wall collapses or contracts beyond vertical and in extreme cases is known to fold over axially. These effects can propagate a cycle of distortion and imbalance having the related effect of worsening the angular deformity which caused the original problem.
For example, in a case of carpal valgus, the medial wall of the affected limb is lined up closer to the vertical line of force (plum line dropped from point of shoulder). As such, the medial wall receives more load and becomes straighter while the lateral wall (which is under loaded vertically) becomes flared or more sloping. Additionally, the region of the foot under the most load grows the slowest. Hence, the lateral wall in this case (less vertical load) grows faster and the medial wall slower, with time. Between trimmings the limb consequently becomes more valgus as the hoof capsule distortion pulls the limb out.
Foot management techniques are aimed at building and maintaining a healthy foot (base of support), where more severe cases require trimming and the addition of an extension. An extension can be an epoxy or acrylic patch with Kevlar fabric that is placed in the heel quarter and extended to a plum line dropped from the condyle of MC/MT III to the ground. Extensions are made out of acrylic, that is, built up around the side of the hoof wall and molded outwards to create an extension. Such extensions, however, create a lever effect on the hoof wall and can create flares and hoof wall separation, as described above.
Treatments using extensions, and the limitations of same, are described in detail within a publication by Scott Morrison, DVM; Morrison, S., FOAL FOOT CARE, CanWest Conference, Oct. 17-20, 2009. Dr. Morrison's disclosure indicates that extension shoes, as an alternative to an acrylic/Kevlar extension, do not pull on a focal area as much as an extension and better distribute the leverage over a larger area. Dr. Morrison explains that while various shoe types can be used to create an extension shoe, aluminum is most common where the extension is directly glued to the bottom of the hoof.
Dr. Morrison explains, however, that while such aluminum shoes are helpful with wide feet, directly gluing such a shoe on a foal foot constricts the hoof to some degree and likely creates a mild heel contracture. Dr. Morrison posits that an indirect gluing method is probably the most effective and least damaging means for gluing an extension shoe, which allows heel expansion and constricts the hoof minimally, if at all. Dr. Morrison then discusses the Sigafoos' series gluing system, wherein flexible fiberglass fabric is adhered to the shoe and the wall to provide a flexible attachment to the shoe.
Such techniques may be said to frequently realize an entirely contracted hoof (i.e., mule footed), which provides poor limb support. At other times, only a half-contracted hoof, usually medially on a valgus deformity and laterally on a varus deformity. Dr. Morrison indicates that there is benefit from widening the foot to a normal shape or widening the contracted half to so that it is pulled out beyond vertical, which is known to be accomplished by use of hinged spring shoes.
A medial extension on one side and toward the back of the foot will support the overloaded side of the limb, i.e., will move the plane of support toward the midline to allow a more even distribution of weight over the support surface. This has the effect of promoting centerline breakover. Extensions constructed from poly methylmethacrylate (Equilox®) and fiberglass are applied directly to the foot by the veterinarian, and shaped to the desired width to provide the exact amount of correction. The extension is trimmed by the veterinarian like normal hoof as the foot grows or additional applications are applied as deemed necessary.
There are significant problems in the use of solid inflexible extension horseshoes, for example, aluminum. The hoof is unable to flex naturally, and change with the redistribution of weight. That is, by fixing the hoof directly to all inflexible surface (as discussed above), the ability of the actively developing young hoof can be inhibited. The inability of a developing hoof to flex limits blood circulation and supply therein, which is so important to the developing hoof of foals, weanlings and yearlings, particularly when the treatment end is to stimulate the limb growth plates without sacrificing the hoof development.
Furthermore, as the developing hoof grows, the rigid extension horseshoes must be changed on a regular basis to allow for these changes. Anytime these therapeutic applications are applied and removed on a regular basis there is hoof wall removed, in some cases more than is being generated (horn growth), particularly with indirect glue cuff shoes (such as taught by Sigafoos, as discussed above) that encapsulate the foot, hoof wall is degraded through the duration of wear and at re-application where hoof wall is removed to prep the surface for a new horseshoe. The therapeutic extension horseshoe as it adapts to the changing young hoof can be left on for longer periods of time.
For that matter, while the problem of wear tends to be insignificant in hard metal extension shoes, extensions made from acrylics, etc., may wear unevenly. And while uneven wear may not significantly affect the foot, per se, it may have a limiting effect on the intended improvement. That is, wear can limit the therapeutic effectiveness of a therapeutic extension shoe.
Laminitis
Laminitis is a disease of the tissue connecting the coffin bone to the inner hoof wall. This tissue is dependent upon continuous blood flow and a supply of nutrients (such as glucose) to maintain this vital attachment. Any process which alters the supply of blood and nutrients to this tissue can initiate the disease process. Laminitis may affect any breed or age of horse, although it is far less common in foals. Laminitis can occur in an individual limb or may affect multiple limbs.
There are many causes of laminitis in the horse. One of the most common causes is carbohydrate overload or “grain founder.” Another common cause of laminitis is endocrine/metabolic disorders. This includes equine Cushing's disease, metabolic syndrome, and insulin resistance. Horses which are severely ill due to some type of systemic disease such as pneumonia, colitis, or endometritis may also develop laminitis. Finally, horses can develop laminitis in a supporting limb if they are very lame on the opposite limb. The foot requires frequent loading and unloading to maintain blood flow. For example, if a case is uncomfortable on the right front limb due to a fractured bone or a serious lameness, the horse will only bare weight on the left limb, and will not intermittently shift weight or unload the foot. Over time, this horse may develop laminitis (from lack of normal perfusion) in the left front limb.
Laminitis can be broken down into several stages. The first is the developmental stage in which trigger factors are released and blood flow changes to the foot occur. This phase is usually set in motion by some other systemic ailment. The laminae are not compromised at this stage. The horse then enters the acute phase. This is defined as the onset of foot pain and at this point an increased digital pulse is easily detected. Most horses then enter the subacute phase and recover with conservative treatment as long as the inciting cause has resolved. The others enter the chronic phase, which is defined as greater than 72 hours of foot pain and/or failure of the lamellar attachments, displayed by coffin bone displacement (rotation, sinking, or both).
Low-Grade Founder
Low-grade founder is an insidious type of founder that develops slowly over the course of months or even years, usually as a result of metabolic imbalance or neglected hooves. A low-grade case of founder is sometimes misdiagnosed as just a bad-footed horse. These horses may have never had an acute episode of laminitis to draw the attention of caretakers. They may never even seem lame. Instead, they may simply seem “ouchy” for a few days in the spring or appear to have a preference for softer footing. Often the problem isn't even suspected until radiographs are taken.
The exterior of the hoof with low-grade founder is likely to appear normal, but a close look at the bottom of the foot and radiography reveal minor but important changes. Usually the white line is stretched at the toe, making the horse more prone to white line disease. When you radiograph these feet there may be a degree or two of coffin bone rotation.
Fortunately, hooves with chronic low-grade founder are fairly easy to manage by just improving the condition of the sole, which in turn supports the coffin bone. If the horse has thin soles that are easily bruised you may just need to thicken up the sole depth. Sometimes just shoeing with a regular keg shoe, a wedge and a rolled toe is all that's required to help the sole become stronger and thicker. Glue is preferred rather than nails to apply the shoes for the first two or three shoeings. Once the sole is thickened, the horse can go barefoot with the edge of the hoof walls rolled.
Where the sole meets the wall it is fairly tough and strong, compared to the inner central part of the sole. The perimeter becomes calloused and strong. With this process of letting the sole thicken by first protecting it with shoeing, the feet grow out beautifully. The cracks in the wall grow out and the foot becomes shiny and healthy rather than dull and shelly; the integrity of the wall changes.
Some experts suggest using sole and frog supports in low-grade cases of founder until the sole naturally thickens. Chronic laminitis horses that have adequate sole depth do very well, but if they lose their sole depth they become uncomfortable and tender very quickly. You can create artificial sole depth, using things like packing or silicone pads.
Cases described as “stable founder” typically have mild rotation or movement of the coffin bone due to persistent low-level inflammation of the tissues. Like low-grade founder, the condition doesn't arise from a single carbohydrate overload after a raid on the feed room, but instead from an underlying physiological problem that continually stresses the structures of the hoof. Nor are these horses likely to have an episode of acute pain, but they are more likely than horses with low-grade founder to be continually tenderfooted and “off.” Stable founder is also more likely to produce exterior evidence of the damage being done inside the hooves. There is more hoof capsule distortion in stable founder than in low-grade cases. The heels grow faster than the toe, and there are founder rings around the hoof. There's more dishing at the front of the foot, and stretching of the white line.
Radiographs will reveal rotation of the coffin bone, caused by the pull of the deep flexor tendon. The rotation isn't typically progressing, hence the term “stable,” but is still the primary consideration in mapping out a shoeing protocol. One of the major shoeing goals is to decrease the pull of the deep digital flexor tendon and rehabilitate the feet. Therefore, the shoe requires some degree of wedge at the rear and also a rolled toe, to take some of the stress off the laminae during breakover.
Breakover is defined as the phase of the stride between the time the horse's heel lifts off the ground and the time the toe lifts off the ground. The toe acts as a fulcrum around which the heel rotates under the influence of the deep digital flexor tendon. The suspensory ligament to the navicular bone and the impar ligament are under maximal stress just before breakover. Changes in toe length, hoof/pastern axis and hoof angle all affect breakover and the tensile forces on the deep digital flexor tendon. In general, breakover is significantly delayed with the presence of a long toe and acute hoof angle because the long toe acts as a long lever arm, requiring more time and forces to rotate the heel around the toe.
In addition, it is believed that tension exerted by the deep digital flexor tendon against excessive toe length results in lamina tearing, which may lead to hoof distortion. The goal of trimming and shoeing the equine foot is to facilitate breakover, ensure solar protection and provide palmar/plantar heel support, no more so than with a horse exhibiting hoof disorders as referenced above. Facilitating breakover, i.e., moving breakover in a palmar/plantar direction, shortens the lever arm created by the toe, changes the tensile forces in the deep digital flexor tendon, moves the navicular bone slightly proximal and changes the angle between P2 and P3. Decreasing the toe length can facilitate breakover by applying a rolled toe shoe.
Although the weight of the horse, transferred through the limb skeleton to the distal phalanx, is considered to be the primary force causing progressive separation of compromised lamellae, additional separation appears to be caused by the rotary force exerted by contraction of the deep digital flexor muscle via the palmar insertion of its tendon (the deep flexor tendon) to the palmar distal phalanx. Therefore, raising the heels of feet affected by acute laminitis by means of a therapeutic shoe with a wedge comprising of 1-3 degrees is claimed to decrease the biomechanical tension in the deep flexor tendon 50-60%, arrest further dislocation of diseased lamellae and to reduce pain.
The club foot is recognized as having strong heel structures and plenty of heel mass; however this foot type can also be affected with chronic heel pain. Since the club foot overloads the toe and bone column, arthritis, sidebone, pedal osteitis of the apex of the P-3, navicular bone sclerosis, osteoarthritis, and contracted heels are common pathologies seen. The compressive forces on the navicular bone are increased as the DDFT (deep digital flexor tendon) is pulled taught against the flexor surface of the navicular bone. It has been shown that upright or club feet have thinner fibro cartilage layer compared to normal feet. Most likely a result of the increased compressive forces of the DDFT against the flexor surface of the navicular bone.
Club feet often have increased wall growth in the heels and slow wall growth at the toe. This is the foot's attempt to raise the heels and unload or accommodate the contracted deep digital flexor tendon. The foot remodels to accommodate all phases of the stride. Since the deep digital flexor tendon is under the most tension just before heel lift off (break over), it is this phase of the stride, which must be addressed when re-balancing the clubfoot. Significantly enhancing/easing break over can allow these feet to return to a normal appearance.
Most club feet can achieve equal toe/heel growth and resolve the anterior dish with these simple mechanics. It is important to realize that the goal is not to fix or resolve the contracture, but merely accommodating it with simple shoeing mechanics and allowing the foot to return to a more normal shape, with even wall growth, no dish, good anterior sole depth, and therefore be a stronger, healthier foot.